From 86ecbc89bd31a80e97ee516ad40178dd4440634d Mon Sep 17 00:00:00 2001
From: "CJACK." <tetr20071102@gmail.com>
Date: Tue, 7 Apr 2026 10:59:27 +0800
Subject: [PATCH] Preserve SSE frame delimiters when injecting Gemini usage

---
 internal/translatorcliproxy/stream_writer.go      | 12 +++++++++++-
 internal/translatorcliproxy/stream_writer_test.go | 12 ++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/internal/translatorcliproxy/stream_writer.go b/internal/translatorcliproxy/stream_writer.go
index b1b8747..e80ce69 100644
--- a/internal/translatorcliproxy/stream_writer.go
+++ b/internal/translatorcliproxy/stream_writer.go
@@ -162,6 +162,13 @@ func injectStreamUsageMetadata(chunk []byte, target sdktranslator.Format, usage
 	if target != sdktranslator.FormatGemini {
 		return chunk
 	}
+	suffix := ""
+	switch {
+	case bytes.HasSuffix(chunk, []byte("\n\n")):
+		suffix = "\n\n"
+	case bytes.HasSuffix(chunk, []byte("\n")):
+		suffix = "\n"
+	}
 	text := strings.TrimSpace(string(chunk))
 	if text == "" {
 		return chunk
@@ -194,7 +201,10 @@ func injectStreamUsageMetadata(chunk []byte, target sdktranslator.Format, usage
 		return chunk
 	}
 	if hasDataPrefix {
-		return []byte("data: " + string(b))
+		return []byte("data: " + string(b) + suffix)
+	}
+	if suffix != "" {
+		return append(b, []byte(suffix)...)
 	}
 	return b
 }
diff --git a/internal/translatorcliproxy/stream_writer_test.go b/internal/translatorcliproxy/stream_writer_test.go
index 77d2936..94d70b8 100644
--- a/internal/translatorcliproxy/stream_writer_test.go
+++ b/internal/translatorcliproxy/stream_writer_test.go
@@ -63,3 +63,15 @@ func TestOpenAIStreamTranslatorWriterPreservesKeepAliveComment(t *testing.T) {
 		t.Fatalf("expected keep-alive comment passthrough, got %q", body)
 	}
 }
+
+func TestInjectStreamUsageMetadataPreservesSSEFrameTerminator(t *testing.T) {
+	chunk := []byte("data: {\"candidates\":[{\"index\":0}],\"model\":\"gemini-2.5-pro\"}\n\n")
+	usage := openAIUsage{PromptTokens: 11, CompletionTokens: 29, TotalTokens: 40}
+	got := injectStreamUsageMetadata(chunk, sdktranslator.FormatGemini, usage)
+	if !strings.HasSuffix(string(got), "\n\n") {
+		t.Fatalf("expected injected chunk to preserve \\n\\n frame terminator, got %q", string(got))
+	}
+	if !strings.Contains(string(got), `"usageMetadata"`) {
+		t.Fatalf("expected usageMetadata injected, got %q", string(got))
+	}
+}